This invention relates to a power source for a nuclear fusion reactor and, more particularly, to a power source adapted to remove a clover element from a bias power supply and to prevent a current from a reversed magnetic field power supply from flowing to the bias power supply side in a nuclear fusion reactor.
FIG. 5 exemplifies a schematic construction of a prior-art power source for a nuclear fusion reactor of this type. In FIG. 5, reference numeral 1 designates a bias power supply in which a capacitor C.sub.B 11 and a diode D.sub.B 14 of a clover element are connected in parallel, one connecting terminal of this parallel circuit is connected through a series circuit of a switch SW1 (12) and an inductor L.sub.D 13 to one end of a toroidal coil L.sub.T 15 of a load coil, and the other connecting terminal of the parallel circuit is connected directly to the other end of the toroidal coil L.sub.T 15. Then, reference numeral 2 designates a reversed magnetic field power supply in which a capacitor C.sub.r 21 and a PFN (Pulse Forming Network) circuit 3 to be described in detail later are connected in parallel through a diode D.sub.p 23, and the reversed magnetic field power supply 2 is connected through a switch SW2 22 in parallel with the toroidal coil L.sub.T 15. The PFN circuit 3 is provided to maintain a reversed magnetic field, and has a predetermined number of parallel capacitors C.sub.p 31 and a plurality of inductors L.sub.p 32 for connecting the capacitors C.sub.p 31 therebetween. The capacitors C.sub.B 11 included in the bias power supply 1 and the capacitor C.sub.r 21 included in the reversed magnetic field power supply 2 are charged in reverse polarity to each other. FIG. 6 exemplifies a waveform of a current flowed to the toroidal coil L.sub.T 15 and the inductor L.sub.D 13 in the prior-art power source.
The operation of the prior-art power source thus constructed as described above will be described. The capacitor C.sub.B 11 in the bias power supply 1, the capacitor C.sub.r 21 in the reversed magnetic field power supply 2 and the capacitor C.sub.p 31 in the PFN circuit 3 are first charged in the polarity exemplified in FIG. 5. The switch SW1 12 is then closed to start discharging the capacitor C.sub.B 11 through the inductor L.sub.D 13 and the toroidal coil L.sub.T 15. At this time, the current I.sub.2 flowed to the inductor L.sub.D 13 is equal to the current I.sub.1 flowed to the toroidal coil L.sub.T 15. This state is continued from the discharge starting time point t=t.sub.0 to the reverse starting time point t=t.sub.1, thereby generating a bias magnetic field of forward direction in the toroidal coil L.sub.T 15. The switch SW2 22 in the reversed magnetic field power supply 2 is closed at the reverse starting time point t=t.sub.1. Thus, a current reverse to that flowed so far starts flowing from the capacitor C.sub.r 21 in the reversed magnetic field power supply 2 to the toroidal coil L.sub.T 15. The current I.sub.1 flowed to the toroidal coil L.sub.T 15 abruptly decreases to cause the polarity to be reversed. Simultaneously, the current from the capacitor C.sub.r 21 is flowed through the diode D.sub.B 14 to the inductor L.sub.D 13 to cause the current to increase.
With respect to a plasma, a plasma current abruptly increases at the reverse starting time point t.congruent.t.sub.1, and a plasma of high temperature and high density has been generated at this time. For example, in order to enclose the plasma of high temperature and high density in a reversed field pinch apparatus, since the toroidal coil included in the pinch apparatus must maintain a substantially constant reversed magnetic field, a substantially constant reverse current from the PFN circuit 3 must be flowed to the toroidal coil L.sub.T 15. Thus, though the plasma is enclosed within a period of time from the reverse completion time point t=t.sub.2 to the main discharge finishing time point t=t.sub.3, the current from the PFN circuit 3 flows to both the toroidal coil L.sub.T 15 and the inductor L.sub.D 13. The inductor L.sub.D 13 is provided to eliminate the abrupt charge of the capacitor C.sub.B 11 in the bias power supply 1 due to the discharge of the capacitor C.sub.r 21 in the reversed magnetic field power supply 2 and ordinarily selected and used to the value of L.sub.D .congruent.(0.5-4)xL.sub.T. The bias magnetic field is several KG to 10 KG, and the reversed magnetic field is approx. -1.0 KG.
In the prior-art power source of this type, the inductor L.sub.D 13 in the bias power supply is excited in addition to the excitation of the toroidal coil L.sub.T 15 as described above. Thus, since the current flowed to the latter is much larger than the current flowed to the former, such a problem arises that the PFN circuit 3 and the capacitor C.sub.r 21 in the reversed magnetic field power supply 2 used for the current must be in large scale. It is further difficult to equalize the time constants of the toroidal coil L.sub.T 15 and the inductor L.sub.D 13. The current flowed to the former is remarkably affected by the influence of the current flowed to the latter to arise a difficulty to flow a constant current. Thus, a ripple as shown by .DELTA.I.sub.1 exemplified in FIG. 6 occurs, with the result that a problem arises that the plasma enclosing characteristic is deteriorated.